Much interest has been shown in essential fatty acids (EFAs) and particularly GLA in recent years, both in relation to prostaglandin (PG) metabolism and generally for the functions of the acids in cell membranes and elsewhere in the body themselves. The two common series of EFAs are the n-6 series, metabolites of linoleic acid, and the n-3 series, metabolites of alphalinolenic acid. The structures and naming of the acids may for example be found in the applicant's published European Patent Specification No. 0132089 (84304610.3). The same specification also contains a discussion of the role of GLA as precursor of 1-series PGs and arachidonic acid as a precursor of 2-series PGs. This discussion is brief but is given at length in earlier applications also referred to and reference may be made to these for the whole background.